Skip to main content

Full text of "Text Book Of Mechanical Engineering"

See other formats

1144                         Appendix VI.

forcing of oil through a small hole in the piston. The springs,
acting differentially, just balance the centrifugal force in all
positions, at one standard speed. If this speed be exceeded, the
dashpot is forced down against the springs K and M to partly close
the throttle valve F. The piston and dashpot would remain in
this new position rigidly, but the oil leaks through the piston, so
as to allow the balls to fly out a little further and so throttle the
steam as to bring the engine back to standard speed. The lever
H can be screwed up to adjust the resistance of the spring M, and
thus alter the standard speed slightly.

Marine Governors are not as much used as they ought to be,
many engineers preferring to prevent racing by hand-adjustment
only. That method is much to be deprecated as quite insufficient
in a stormy sea, when, to adjust the steam supply with any effect
at all, the engine speed must be cut down about half in the first
place. There are three methods of automatic governing at
present on the market: (i) where the action is obtained from the
movement of the hull itself, as at p. 657 ; (2) where some form
of balanced centrifugal governor is adopted; and (3) when a
hit-and-miss arrangement is provided as on many gas engines.
The last-mentioned is very little applied as yet. The second
method will now be described by reference to Fig. 1013, which
shows Murdoch's governor as made by Mr. John Cochrane of

The pulley E rotated by cord from the engine, drives the balls
c c and D D, together with the flywheel A, as one solid mass; but
if the speed is suddenly increased, the bevel wheel over-runs the
flywheel and the balls fly outward, turning on the pins B B. The
right-hand balls, being connected at F to the sleeve G, raise the
ball-crank H and rod K, thus causing the valve L to rotate and
admit steam to the back of piston p while exhausting from the
opposite end of the cylinder N ; and the eye Q, connected to the
engine throttle-valve, partly closes the latter. At the same time
the lever it is moved rightward, to act on spindle s and bring
back the valve L laterally to the closed position. The valve is
shewn below to consist of two compartments, one for admission
and one for exhaust, a helical slot or port being provided in each
iialf; and the cushion j receives the sleeve on the return of the